Project Summary Interpersonal functioning is vital across a range of mental health outcomes, with particular significance for adolescent girls. Adolescence is a critical period for promoting or hindering development of adaptive interpersonal functioning due to dramatic changes in social behaviors and significant maturation of brain regions that facilitate social-emotional processing. Despite this importance, very few prospective, longitudinal studies have used repeated functional neuroimaging data to chart the trajectory of connectivity of social-emotional brain regions across adolescence. The proposed project is rigorously designed to use the Research Domain Criteria (RDoC) framework for Social Processes to address a gap in the field about how functional connectivity of social- emotional brain regions during introspection changes within the same girls across several years of adolescence. First, we will characterize trajectories of connectivity between the mPFC, precuneus/posterior cingulate cortex, and bilateral middle temporal gyrus across ages 16-18. We will then determine if change in functional connectivity from age 16 to 18 promotes or hinders girls' effective interpersonal functioning at age 18. Finally, we will test whether girls' emotion expression and emotion socialization experiences across ages 9-13 moderate the association between trajectories of brain connectivity and interpersonal functioning. We capitalize on an unprecedented existing dataset of neuroimaging, psychosocial functioning, and social-emotional behavior collected on 185 girls from the ages of 9-18 years who are part of the Pittsburgh Girls Study of Emotion. The project will investigate multiple units of analysis (e.g., circuits, paradigms, behavior, self-reports) of the RDoC Affiliation and Perception/Understanding of Self and Others constructs, and situates these units of analysis in the context of neurodevelopment and environmental experiences. Several aspects of the proposed study will allow us to generate highly impactful data. First, the sample size would be one of the largest to date for examining trajectories of task-based functional connectivity (e.g., latent growth, moderation). Second, potential findings can inform the development of more precise treatments and interventions designed to target affective processes, socialization and interpersonal functioning of adolescent girls at risk for psychopathology. Third, assessments of emotional socialization, emotion expression and self-reported interpersonal functioning are completed within each subject, providing an opportunity to test more refined models of how functional connectivity underlying psychological processes may become disrupted and lead to poor interpersonal functioning. Fourth, leveraging existing prospectively collected data provides an unprecedented, and economical, test of individual factors that may moderate brain-behavior associations. This will be one of the most comprehensive and rigorous tests of the associations among early adolescent emotion socialization and emotion expression, trajectories of brain connectivity linked to introspection across adolescence, and interpersonal functioning in young adulthood.